1. Field of the Invention
The present invention relates to a vibration measurement system for a rolling bearing which measure vibration, that is, displacement, velocity, acceleration change and elastic wave of a rolling bearing.
2. Related Art
A conventional known vibration measurement system of a rolling bearing comprises drive device for rotating an outer or inner ring, a vibration pickup for detecting vibration or an elastic wave (hereinafter, the "vibration" contains elastic wave) of the outer or inner ring, and a frequency converter for analyzing a signal detected by the vibration pickup.
The vibration measurement system analyzes detected vibration, that is, displacement, velocity, acceleration change and elastic wave (AE signal) and, for example, checks the bearing ring which is an inner or outer ring of a rolling bearing or the rolling face of a plurality of rolling elements, i.e., roller or ball, for flaw, surface roughness, waviness, defective form, foreign material, etc., and monitors an abnormal condition occurring on the bearing in an endurance test, etc.
For a bearing having no contact angle, such as a cylindrical roller bearing, needle bearing, or water pump bearing of ball or roller type, the conventional vibration measurement system imposes a radial load or a moment load on an outer ring and locally removes clearance between a rolling element such as a roller and a bearing ring, then in this state, drives the bearing for executing vibration evaluation of the bearing unit. For a bearing having a contact angle, such as a ball bearing, the vibration measurement system drives the bearing for executing vibration evaluation of the bearing unit in a state in which an axial load is imposed in accordance with the dimensions of the bearing.
However, the conventional rolling bearing vibration measurement system suffers from the following problems: Although a load zone with no clearance between the rolling element and the bearing ring can be formed by imposing a radial or moment load locally on the outer ring in a bearing such as a roller bearing having no contact angle, a non-load zone in which clearance occurs between the rolling element and the bearing ring is formed in other portions. If the bearing is driven in the state, a phenomenon of so-called roller drop occurs in which the rolling element collides with the bearing ring on the boundary where the rolling element moves from the load zone to the non-load zone, causing impulsive vibration to occur. FIG. 8 is a graph of measured vibration signal. A large peak signal i is caused by impulsive vibration and is mixed with evaluation information such as a rolling face flaw, thus making bearing vibration evaluation difficult to execute. Even if shock is comparatively light, roller slide, etc., makes correct evaluation difficult to execute.
Further, for evaluation over a full periphery of a fixed ring, the conventional vibration measurement system may rotate the fixed ring little by little and move the load zone, but the total measurement time is prolonged and the vibration measurement system needs to perform complicated control because of repeating the steps of rotating the fixed ring and then executing measurement.
On the other hand, to fit a bearing such as a ball bearing having a contact angle to an actually used machine, a close fit is often used for creep prevention during operation. In such a state, elastic deformation to the inner or outer ring side is made, thus the contact angle decreases and the running position of a rolling element such as a steel ball is shifted to the groove center of a bearing ring. The difference between the contact angle during vibration evaluation of the bearing unit and that in practical use is often at stake. Up to now, effective countermeasures have not been provided.
To solve the problems, extremely accurate working is required for finishing the dimensions of the fit part of a rolling bearing to be measured (the outer diameter of a mounting shaft into which an inner ring, etc., is fitted and the inner diameter of a housing to which an outer ring is attached) to the dimensions to allow the bearing clearance when the rolling bearing is fitted to become a predetermined value (zero when the rolling bearing has no contact angle or a clearance distance to allow the contact angle to become a preset angle with a predetermined axial load imposed when the rolling bearing has a contact angle). Although the design dimensions are the same, the dimensions vary from one rolling bearing to another. Each time the measurement object changes, the fit part must be matched with it. Further, if an interference is made too large, deformation affecting the bearing ring and rolling element forms, etc., occurs and correct evaluation may be unable to be executed.